Dogs are like kids - everyone has their own way of doing it and whilst there might some key fundamentals we all agree are right or wrong, there are huge variations of the more complex and greyer areas. I might decide that I would not be happy keeping a dog in x way but someone else may well be able to keep the right dog, happily like that.
I wouldn't change that here because it is a forum, a place for debate. A place to gather opinions but not necessarily agree with all of them.
Ultimately, though, it'll be the dog that 'decides'. There are as many different dog personality types as there are people. It'll either cope with with being left or it won't. A good question to ponder would be, what'll you do if it cannot cope?
The big call out I would make is, to use the logic "I know loads of happy dogs who are left all day" is to only see half the picture. Of course they are happy. The chances are, they would have been rehomed if not. There tends to be only so long someone can come home to poo everywhere or a chewed up carpet or holes in the wall, before they take the dog to a shelter and surrender it because they cannot give it the time. People also tend not to tell too often if they have ever had to rehome a dog because they couldn't cope. The bit of volunteer work I have done with dog shelters, that and intolerance to children seem to be the top reasons. It seems likely to me, then, that the dogs that remain in the family home are the ones who can cope. The RSPCA did some research and found that 80% of dogs display stress behaviours when left alone (obviously to massively varying degrees) but in only 50% of cases could the owners recognise the dog was stressed. That would further suggest that the not all the 'happy' dogs are happy. They are just not the kind of stressed that gets them rehomed.
Of course, there are also genuinely happy dogs who spend time alone each day. I suspect they biggest influencing factor, after the dog's personality, is how much effort their owners put in outside those times.
Anyway, just food for thought. If only to add 'research stress behaviours' to your list of things to learn about in advance 
With regards to picking any breed, my top tip would be to read the worst about that breed and be sure you can cope with it, if is happens. If looking at cross breeds then read the worst of BOTH breeds and be prepared.
A labradoodle (just using your example) could be a relaxed, intelligent, easy to train and loving dog. The best of both. Or it could be an energetic, chewy, needy, hates to be left alone, too smart to easily entertain pita. Be prepared for the worst of both breeds to know you can cope with whatever comes your way.
It is also true that finding a decent breeder for a cross will be harder than a pedigree - because you will struggle for a decent starting point. With pedigree dogs you can use the breed club and KC to get a list of breeders and then apply your own checks to weed out the good from the bad. With crosses that starting point isn't available to you, so you start from cold. They are also popular and popularity always attracts people just in it for £. You would have a similar problem re popularity with frenchies, chis, pugs etc.
Have a look at www.facebook.com/groups/374160792599484/